In the Long Term Evolution (referred to as LTE) system, after be powered on, the mobile terminal first performs the downlink synchronization through the synchronization Channel (referred to as SCH), to determine the receiving starting point and the cell number (cell ID) of the wireless frame and subframe; and then obtains the system information through detecting the Broadcast Channel (referred to as BCH), and the system information includes the configuration information of the Random Access Channel (referred to as RACH), and finally, the uplink synchronization is performed on the random access signal transmitted by the RACH, to complete the work of accessing the system.
In the process of the uplink synchronization of the mobile terminal, the location of the RACH is first found based on the receiving starting point of the wireless frame and sub frame determined during the downlink synchronization, and the starting point for sending the uplink random access preamble is determined, and then one sequence is selected randomly from the available sequences as the uplink random access preamble of the random access signal for transmission. The base station detects the uplink random access preamble, to determine the timing adjustment amount of the uplink synchronization, and sends it to the mobile terminal; and the mobile terminal adjusts the sending time of the uplink signal according to the timing adjustment amount, to achieve the time synchronization of the uplink channel.
The uplink random access preamble in the existing LTE system is generated by one or more Zadoff-Chu (ZC) root sequences. The uth ZC root sequence is defined as
                    x        u            ⁡              (        n        )              =          e                        -          j                ⁢                              π            ⁢                                                  ⁢                          un              ⁡                              (                                  n                  +                  1                                )                                                          N            ZC                                ,0≤n≤NZC−1. Herein, the length of the ZC sequence NZC is 839 under the formats 0-3, and is 139 in the format 4. There are 64 sequences used to generate the uplink random access preamble in every cell, and the 64 sequences can not only be various cyclic shift sequences from the same root sequence, but also can be the cyclic shift sequences from different root sequences. The ZC root sequence is a Constant Amplitude zero Auto-correlation Code (referred to as CAZAC), and its correlation has the following characteristics: the correlation among different cyclic sequences of the same root sequence is 0; and the correlation of different root sequences (including their cyclic shift sequences of each other) is 1/√{square root over (NZC)}, that is, the correlation between the uplink random access preamble of the random access signal and the rest of the sequences is very small, which can be regarded as approximately equal to zero, while the correlation between the uplink random access preamble of the random access signal and the sequence generating the preamble is maximum. Therefore, the method in which the correlation between the uplink random access preamble random access signal and all sequences of the random access signal can use in time domain detection to judge the random access preamble transmitted by the terminal, and then obtain the uplink timing adjustment amount, realize the time synchronization of the uplink channel.
The existing method for detecting the random access signal has the problem of higher index of leak detection or false detection in the interference environment. When there is a larger interference from the adjacent cell, the signal peak in the existing method for detecting the random access signal will be drowned in the interference and noise, which leads to the leak detection; at the same time, a wrong peak is detected because of the impact of interference, leading to the false detection. In addition, when there are signals with large and small power coexisted in the present cell, the signal with the large power is the interface of the present cell relative to the signal with the small power, which will enlarge the possibility of leak detecting the 1 signal with the small power. Some existing methods of serial interference cancellation first subtract the reconstructed interference signal from the received random access signal, and then perform the detection, and subtract a reconstructed useful signal again from the received random access signal when every useful signal is detected, and then perform the detection. That type of methods must first know the interference signal, which has a high requirement for the system; and secondly, it needs multiple times of reconstruction, which occupies a large amount of resources; the computation is very large, and is difficult to be realized and applied.
In short, the existing technology has at least the following shortcomings: the method for detecting the random access signal does not consider the interference effect, there are problems of higher index of leak detection or false detection in the adjacent cell interference environment, at the same time the requirement to the system is relatively high, the occupied resources are large, and it is difficult to be achieved and applied.